1. Field of the Invention
The invention relates to a smoothing method to decrease bowing of group III nitride semiconductor substrate, particularly to a smoothing method to decrease bowing of group III nitride semiconductor substrate by using an etching method.
2. Description of the Prior Art
In the manufacturing process of conventional photoelectric semiconductor element and electronic element semiconductors, particularly in the manufacturing process of single crystalline gallium nitride substrate (free-standing GaN substrates), the severe bowing phenomenon will be occurred on single crystalline nitride epitaxy layer during the heating process, due to the expansion coefficient between the heterogeneous substrate under this single crystalline nitride epitaxy layer is not matched.
In the parallel direction, the uneven line defects and point defects will be generated on the group III nitride semiconductor substrate adopted by the above-mentioned process, resulting in the bowing of group III nitride semiconductor substrate. The bowing radius is about 0.2 m to 2 m. As for 2 inch free-standing GaN substrates, the deviated distance between the centrality to the edge may be 1500 μm to 150 μm. Sometimes the deviated distance is even larger than the thickness of free-standing GaN substrates. The bowing phenomenon of free-standing GaN substrates or nitride epitaxy layer will cause the grinding rupture and uneven grinding phenomenon between the substrate and epitaxy layer, which becomes a problem waiting to be solved urgently.
In addition, in the prior art of the photoelectric semiconductor element and electronic element semiconductor technology, the methods for improving the bowing of group III nitride semiconductor substrate includes the following methods:
In Taiwan Patent No. 200423312, a selective growth of patterned nitride seed was proposed, but this method requires tedious yellow light process, and the reduction for the bowing of free-standing GaN substrates is limited, even the bowing phenomenon of free-standing GaN substrates cannot be measured in time for flexible adjustment.
In U.S. Pat. No. 7,229,926, a mechanical grinding method was proposed to grind both sides of substrate, and the dry/wet etching method was used to remove the damaged layer generated by the grinding. But this method will not decrease the bowing phenomenon of substrate, so it will result the rupture of substrate and uneven phenomenon of substrate upon grinding. This method has to grind the generated damage layer, and then the etching can be conducted to decrease the bowing phenomenon of substrate.
Summarized from the above-mentioned patents, the prior art has not mentioned the improvement level for the bowing phenomenon of free-standing GaN substrates as the heterogeneous substrate below the free-standing GaN substrates has not been removed.
Therefore, in order to the bowing phenomenon of free-standing GaN substrates more effectively, provide the industry to grasp better production process for applying in the photoelectric semiconductor element, it is necessary to research and develop innovative method to increase the yield for the production of free-standing GaN substrates and reduce the manufacturing cost of photoelectric semiconductor elements.